This invention relates to fingerprinting, and is particularly concerned with a novel fingerprint powder, particularly a fingerprint developing powder having high sensitivity, and to a method for developing or recording latent fingerprints employing such powder.
Various compositions and methods have heretofore been employed for developing or recording latent fingerprints. The conventional procedure for developing a latent fingerprint involves applying to the surface having such fingerprint thereon a small amount of a finely powdered solid material until the outline of the fingerprint becomes visible and then carefully spreading the applied powder over the fingerprint in order to bring out its pattern. Various substances including powdered metals such as aluminum and bronze, dragon's blood powder, a gray powder consisting of finely ground French chalk and mercury, and a black powder having a lampblack or charcoal base have been employed for this purpose.
However, the powder compositions heretofore employed have certain disadvantages. Of particular note, many of the prior art fingerprint powders are not sufficiently sensitive and do not provide the desired contrast to clearly bring out the fingerprint pattern, so that hand and fingerprints thus obtained lack clear visibility. Further, some of the prior art fingerprint powders have an abrasive action which tends to streak and/or obliterate the latent fingerprint when such powder is applied to the surface containing such fingerprint. Further, a brushing technique is generally employed with conventional powders, and development of fingerprints employing such prior art technique and powders is often difficult and time consuming, and requiring considerable skill, while at the same time avoiding waste by use of excess powder.
As exemplary of the prior art methods for fingerprint detection, are the following patents: U.S. Pat. No. 1,259,981 discloses the use of a powder for fingerprint detection containing a pigment and an adhesive. U.S. Pat. No. 3,132,036 discloses developing a latent fingerprint on a surface by applying to the surface a layer of opaque magnetizable powder and passing a magnet across the layer of powder. The patent also discusses the prior art use of iodine vapors for latent fingerprint detection. U.S. Pat. No. 3,075,852 discloses use of a powder for fingerprint detection, in admixture with a liquefied gaseous propellant.
In my copending application Ser. No. 649,293, filed Jan. 15, 1976, there is disclosed a dry powder indicator composition for detecting cracks and leaks in a component of a fluid-filled system, containing talc and silica as a carrier powder, and a coloring agent, which can be a fluorescent dye.
It is an object of the present invention to provide novel compositions and procedure for developing latent fingerprints on a surface. It is a particular object of the invention to provide a fingerprint powder which can be readily and rapidly applied to a surface containing latent fingerprints, without use of excess powder, and containing a coloring agent, such that the developer powder has high sensitivity, and to a method for rendering visible or detecting and developing either old or fresh latent fingerprints on a surface, employing such fingerprint powder, to obtain bright, sharp fingerprint patterns of high contrast and resolution.